The Cellar after Harvest’s Dust Settles
By: Denise M. Gardner, Enology Extension Associate
Most likely, all of the wines from the 2016 vintage are happily settling away in tank or barrel at this point. After such a busy time, his leaves winemakers with that tricky question, “What do I do now?”
Monitoring Malolactic Fermentation (MLF)
Now is a good time to make sure you are monitoring your malolactic fermentations. Ensure all of your barrels or tanks have been appropriately inoculated, or have started naturally, and get some initial readings on the malic acid concentration.
If you have a spectrophotometer, you can purchase enzymatic kits to measure the concentration of malic acid in your wine over time. Wines with less than 30 mg/100 mL of malic acid are considered “dry” for MLF or MLF-stable for bottling.
However, winemakers can also monitor malic acid degradation through the use of paper chromatography kits. These kits are easy enough for home winemakers to use and can also be applied at the commercial level.
Paper chromatography works by separating tartaric, malic, and lactic acids from a wine sample (Figure 1). In addition to blotting small drops of your various wine samples, each paper must also contain 3 standards to show the spots documented by the three acids (tartaric, malic, and lactic). While paper chromatography is not the best at concentrating how much of each acid remains in the wine, you can get an idea when the bulk of malic acid is converted to lactic acid (i.e., MLF is completed) when the malic acid spot associated with the wine samples disappears.
For a complete protocol on paper chromatography, please see this page: https://www.midwestsupplies.com/media/downloads/421/malolactic_chromatography_kit.pdf
Checking Wines for Off-Flavor Development
It’s also a good time to check wines for hydrogen sulfide (H2S) or sulfur-base off-odor aromas, and volatile acidity (VA), especially for wines that you will want to bottle early in the new year.
Hydrogen sulfide can be treated with copper sulfate. Penn State Extension offers a great 2-page fact sheet on how to run a copper screen to determine if the wine requires copper sulfate, and a copper bench trial in order for you to assess how much copper is needed to treat the hydrogen sulfide: http://extension.psu.edu/food/enology/wine-production/wine-made-easy-fact-sheets/sulfur-based-off-flavors-in-wine
Now is also a good time to know what the VA is in your wines, especially those that will be seeing some aging. This is incredibly important to get a baseline value of the VA. That way, if a problem emerges in the future, you will have an indication how much the volatile acidity has increased. Penn State Extension also offers a 2-page fact sheet explaining why knowing volatile acidity is important, provides protocols for its analysis, and how to mediate high VA situations: http://extension.psu.edu/food/enology/wine-production/wine-made-easy-fact-sheets/volatile-acidity-in-wine
If you are having problems identifying these key defects in your wine, don’t forget that the annual “Wine Quality Improvement” Short Course is just around the corner in January. For more information on this workshop and its registration, please go here: 2017 Wine Quality Improvement (WQI) Short Course
Now is also a good time to clean up any leftover sore spots from the chaotic harvest season:
- Clean up places in the cellar that have gotten dirty or have become areas that are accumulating materials that should otherwise be put away.
- Manage all of your harvest records. Make sure all of the wines have the basic wine chemistries (e.g., pH, TA, residual sugar, alcohol, free and total SO2, malic acid, and volatile acidity) in the record book. It is easy to forget all of these details as time progresses.
- Make sure wines are properly stabilized for storage. Treat wines appropriately with sulfur dioxide. If you need some tips on sulfur dioxide management, refer to Penn State Extension’s Wine Made Easy fact sheet: http://extension.psu.edu/food/enology/wine-production/wine-made-easy-fact-sheets/sulfur-dioxide-management
- If you know you need to move wines off of lees, now is a good time to go through each tank one-by-one and make the necessary adjustments.